1. Field of the Invention
The present invention relates to wireless telecommunications in general and more particularly to a method and system for determining a direction of arrival angle with a smart antenna in a wireless telecommunications system.
2. Related Art
A smart antenna, such as a blind adaptive antenna array, is a method and system used to enhance a desired user signal, to suppress multiple access interfering signals, and in general to improve the performance of a wireless communications system, including CDMA systems such as third generation (3G) wireless communication systems, particularly those specified in the wide band CDMA (W-CDMA) or the CDMA2000 standards. In such systems, smart antenna technology may optionally be employed at a base station. A smart antenna can suppress interfering signals of different DOAs (Directions of Arrival) by using spatial diversity. Smart antenna technologies attract much attention these days as they support more users with a high quality of service and high data rates. Efficient smart antenna schemes have appeared recently. It is desirable that a smart antenna be effectively easy to implement.
The DOA tracking capability, convergence, and computation complexity are very important issues in the design of the smart antennas. Conventional methods for determining the direction of arrival of an incoming signal in a smart antenna system require matrix computation or complex computation, which are the costly parts of the smart antenna tracking algorithms. Specifically, known algorithms attempt to calculate the weight vectors directly by minimizing or maximizing some cost criteria such as SINR (signal to interference+noise ratio), BER (bit error rate) or MSE (mean square error). These methods require determining a separate weight vector for each antenna element; e.g., if there are six antenna elements, six unknown variables must be determined. Another drawback associated with known methods is that practical embodiments of these methods require calibration of mixer phase distortions.
The aforementioned needs are addressed to a great extent by the present invention, which provides a method and system for performing an initial DOA estimate and fine-tuning the estimate and for tracking the DOA when there is relative motion between the transmitter and receiver. The present invention utilizes the notion that the maximum antenna gain can be achieved when the weight vector for the antenna array is matched to the array response vector. In highly preferred embodiments, rather than attempting to calculate the weight vectors directly as is done in conventional algorithms, the present invention estimates a DOA angle and calculates the weight vectors as a function of the estimated DOA angle. The estimated DOA angle is then adaptively updated to optimize correlation output, e.g., to achieve the maximum output power or maximum signal-to-interference-plus-noise-ratio (SINR) for the desired user. This method may be used during both the initial search for the DOA, in which a coarse adjustment is made to the estimated DOA angle, and for tracking the DOA as relative movement between the transmitter and the receiver occurs, in which a fine adjustment is made. The proposed algorithm of the present invention is not sensitive to mixer phase distortions. Thus, a separate phase calibration is not required in the system. The proposed algorithm also has lower computational burdens, as compared to conventional algorithms, for calculating weight vectors for smart antenna arrays, thereby lowering the complexity and cost of a system.